1. Field of the Invention
The present invention relates to an elastic wave device and a method for manufacturing the elastic wave device.
2. Description of the Related Art
In the related art, elastic wave devices have been widely used.
For example, in a surface acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2008-124785, via electrodes are provided so as to extend through a support layer, which is provided on a piezoelectric substrate, and a cover member, which is disposed on the support layer. Each of the via electrodes includes a first via electrode portion and a second via electrode portion that extends to the first via electrode portion. The first via electrode portions extend through the support layer. The second via electrode portions extend through the cover member. In Japanese Unexamined Patent Application Publication No. 2008-124785, the diameter of each of the second via electrode portions is larger than the diameter of each of the first via electrode portions.
In the related art, as described in Japanese Unexamined Patent Application Publication No. 2008-124785, the contact areas between via electrodes and outer electrodes need to be large in order to improve thermal shock resistance and the like. However, in Japanese Unexamined Patent Application Publication No. 2008-124785, the lower ends of the second via electrode portions, each of which is connected to a corresponding one of the outer electrodes and each of which has a large diameter, are in contact with the support layer. In other words, since the cross-sectional area of a lower end portion of each of the second via electrode portions is large, the dimension of the support layer, which is located below the second via electrode portions, in a width direction also needs to be large. Meanwhile, the surface acoustic wave device includes a hollow portion that is formed of the piezoelectric substrate, the support layer, and the cover member. The plane area of the hollow portion needs to be sufficiently large in order to accommodate IDT electrodes, a filter circuit including IDT electrodes, and the like. However, in Japanese Unexamined Patent Application Publication No. 2008-124785, since the dimension of the support layer in the width direction needs to be large, it is difficult to facilitate a reduction in the size of the surface acoustic wave device.